Transformer tap-changing system



May 14, 1940- L. F. BLUME 2,200,979

TRANSFORMER TAP-CHANGING SYSTEM Filed June 22, 1939 Inventor! Louis F. Blume,

JV H35 Atbtjr'ney.

Patented May 14, 1940 UNITED STATES PATENT OFFICE Louis F. Blume, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application June 22, 1939, Serial No. 280,567

9 Claims.

- This invention relates to a method and apparatus for transformer tap-changing-underload and more particularly to an improved vernier type load ratio control system.

By load ratio control is"meant the control of .the voltage ratio of a transformer under load by means of suitable tap-changing switches. A .vernier load ratio control system difiers from an ordinary load ratio control system in that a vernier winding is selectively connectable between taps on the main transformer winding and taps are changed on the vernier Winding so as to give a plurality of intermediate steps or voltages between the voltages of the taps on the main transformer winding. By successively connecting .the vernier Winding across difierent pairs of main winding taps the number of voltage steps is many times greater than the actual number of taps employed. Thus, the number of steps is equal to the. product of the number of pairs of taps on the main winding and the number of pairs of taps on the vernier winding instead of beinglequal merely. to the sum of the number of 'taps'onzboth windings.

In accordance with this invention I provide :two insulated vernier windings and operate the tap-changing means on the main transformer .and on the vernier windings in such a way that the main transformer tap-changing means is operated only when it is not carrying current. It can therefore be operated slowly and the usual switch or contactor for interrupting the current in the main tap-changingmeans before a tap- -changing operation takes place can be eliminated.

An object of the invention is to provide a new and improved method and apparatus for transformer tap-j-changing-under-load.

1 {Another object of the invention is to provide .an' improved and simplified vernier load ratio icontrol circuit.

The invention will be better understood from .the following description taken in connection with-the accompanying drawing and its scope will be pointed out in the appended claims.

In. the drawing, in which like reference characters designatethe same elements in the two views, Fig. 1 illustrates diagrammatically an embodiment of the invention which may be manually operated, and Fig. 2 illustrates a complete automatic mechanism for carrying out my invention.

Referring now to the drawing, and more particularly to Fig. 1, there is shown therein a main .-transformer windingl which may, for example,

be one of the phase windings of the primary or the secondary of a transformer system having any number of phases. The circuit of this winding may be completed through a conductor 2 and ground 3. The winding I is provided with a plu- .15 rality of taps 4 terminating in tap contacts 5. For engaging these tap contacts are a pair of main movable contacts 6 and- I.

A pair of insulated vernier windings 8 and 9 are connected respectively to the main movable .10 contacts 6 and 1. These vernier windings may be mounted on the same core as the main winding l or they may be excited by a separate core if desired. They are each preferably, but not necessarily, provided with a plurality of taps Ill 15 terminating in vernier tap contacts H. Taps are changed on the vernier windings by means of a pair of movable vernier contacts l2 and I3 which are connected respectively to the terminals of a mid-tapped reactor M of conventional design for minimizing circulating current flow in the vernier winding. The mid-tap of reactor I4 is connected to ground 3.

The taps 4 on the main winding are preferably substantially equally electrically spaced so that 25 the voltage between each adjacent pair of them is substantially equal. Similarly the taps l0 on the .vernier windings are preferably substantially equally spaced so that the voltage between each adjacent pair of them is substantially equal. However, the voltage between adjacent vernier taps is less than the voltage between adjacent main taps. In addition, the sum of the voltages of the vernier windings 8 and 9 is preferably less than the voltage between adjacent taps 35 on the main winding. This difference is preferably equal to the voltage between a pair of adjacent vernier taps ID.

The operation of Fig. 1 is as follows. If it is desired to connect more of the main winding l between conductor 2 and ground, vernier contact I3 is moved downwardly from the position shown. In this new position, the mid-tapped reactor I4 is connected between the two lowermost .tap contacts on the vernier winding 8 and a cirthe two halves of reactor H in parallel. As there :is no voltage across the reactor N, there will be 55 able contact l2.

no circulating current in it; and as the load current will divide equally between the two halves of the reactor, it will have substantially no effective reactance. The contacts l3 and I2 are then moved to the first contact on Vernier winding 9 in the same step-close order, contact l3 leading and contact l2 following up and closing the step. It will be observed that when the verniermovable contacts are transferred from Vernier 8 to Vernier 9, the load current is transferred from movable main contact 5 to movable main contact l.

For the first step in tap-changing described above, between the next to the last and the last tap contact on Vernier .8, the voltag'e between these taps is added to the voltage of the top main tap contact on the main winding. When the contacts l3-and"l2-make"contact with the Vernier tap contacts on the; vernier winding 9, the voltage of the Vernier winding 9 is subtracted from the voltage of the 'main tap contact to which the main movable contact I 'is connected. However, asthe' voltageof this latter main tap contact is greater than the voltage of the first or upperniost main tapcontact,

'the change in voltage is the same for each step made on the vemier windings; When the'vernier movable contacts" and l3-hav'emo'ved'down to one of the tap contacts on the Vernier winding 9, the main movable contact 8, which-now is carrying no current,'is moved-down into engagement with the same tap contactto which the main l3 intoengagement with thetopmost tap contact on the vernierwindingt-and-then follow-it up'by'making-the same tap change-with the mov- When {this"' s tep' completed, the load currentywi'li saw" through "the' in0vable 'main contact 6, and themovable main contact "1 will be'idle. As :main movable contacts fi and I are both in engagernent withthe'same main tap contact, the only voltageproduced-by thislast Vernier tap changeis to raise the-voltage by the tap to tapvernierf'voltage represented-by the end turns on the verifier-winding '9. -The 'vernier movable contacts arethen'QmoVed downwardly again over the tapcontacts'ofthe' Vernier winding 8, and when they reach one 'oi the inner or central tap contacts'themainmovable contact I is moved downto the main'tap contact. The elements will now beiin the same relative positions they occupy in Figil except that main movable contacts '6 and 'I have each beenmoved 'down' one tap. This'cycle *of operation may be continued as long as desired and-if it isdesired to change the voltage in the opposite direction tacts 6 and l are only moved'at times when the Vernier movable contactsare in engagement with the vernier tap contacts on theverniefwinding which is connected to'thej other movable .contact. Consequently, the main movable contacts are never called upon to" break any current and they can. be movedfslowly' irom tap to tap and it is unnecessaryto provideany additional contactors or current interrupting means for these movable contacts.

As the sum of the voltages of the Vernier windings 8 and 9 is less than the tap to tap voltage on the main winding by an amount which is equal to the Vernier tap to tap voltage, it follows that, when the Vernier tap-changing contacts l2 and I3 go from the lowermost tap contact on Vernier winding 8 to the: uppermost tap contact on Vernier winding 9, the voltage change will be equal to the Vernier tap to tap voltage. Consequently, so far as voltage changes in the main circuit are concerned all the vernier voltage steps will be substantially equal.

Another feature of the invention is that there will normally be no circulating current in the main winding when the main movable contacts 6-and1 are in engagement with different main tap contacts 5. This is because the Vernier windings 8 and 3 are insulated so that only when the -vernier movable contacts 12 and I3 bridge the gap between the Vernier windings 8 and 9 will it be possibleqfor any circulating current to flow in the main winding I.

InFig. 2 the movable contacts-6, 'I,.:| 2.and l3 and-the tap contacts 5 and "II are. arranged to form separate dial type switches or ratio .adjusters. They are arranged to be operatediin the proper sequence automatically by means of suitablemechanicalv movements shown by way of example as Geneva gear movements [-5 operated' by a common driving motor 118. The movable contacts 12 and 13 are continuously rotatable making :one complete revolution corresponding to one complete tap-changing cycle in Fig. l.

'As there are nine vernier tap contacts shown, the vernier tap-changing contacts'lzzand' [30peratenine times as fast as theimaint'ap changing means 6 and 1 so that a 911 gearireduction is interposed between the drive zfor :the ve'mier tap bhangersflandl3 andnthe main tap changers '6 and-:7 This -is shown xiiagr'ammatically byLreeduction gearing fl land an aidlerigear ilfl hasbeen inserted so that the direction of rotatione-oflall of the Geneva-gear movements will appearthe and thus' render easier rthe understanding of the operation. 4 4. s-s

= A contactor i9 driven by 9. Beam 2!] has also been provided. for automatically interrupting "the current throughthe vernieriap changers-Hand 1-3 before-"they make a tap-changingioperation. 'I'he'operation of Fig.2 is as follows: The parts in Fig. 2am I electrically in the sameirelative p0 s'itions as they are shown in Fig. L JWhen motor I8 is energized so as to drive the cams in the direction shown by the-arrows, the left hand contact 0f contactor- 19 will first open ihen the Vernier tap changer 13 will the .rotated 7013651381) in a counter-clockwise direction.-.I?Ihenthe-1efthandcontacts of the contactor. I8 will close. Next the right-hand contacts of conta'ctor- 19 will open --'and shortly thereafter the wemier. tap

change? 12 will make its'iollow-up'motion and changer lis connected. The operation then contiziuesi'or about another half revolution of -'the Vernier-tap switches l2 and I3 and at about one tap or step in a counter-clockwise direction.

This cycle will 'then continue as long as desired and of course may be reversed at any time; The main 'tap changers 6 and I always operatewhen they are not carrying any current so that they may operate without any difficulty at one-ninth the speed of the vernier tap switches l2 and 13. While there have been shown and described particular embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the invention and, therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The method of transformer tap-changingunder-load which comprises, first, providing a movable two-contact type main tap changer with a pair of insulated tapped vernier windings connected respectively to the'main movable contacts; second, making successive main-circuit connections to the taps on one 'vernier winding and moving the movable contact connected to the other vernier winding during said successive connections; and, third, making successive main-circuit connections to the taps on the other vernier winding and moving the first movable contact during said second successive connections.

2. A transformer ratio adjusting system comprising, in combination, a main transformer winding provided with a plurality of main tap contacts, a pair of movable main contacts for successively engaging said main tap contacts, a pair of insulated vernier windings connected respectively to said main movable contacts, said vernier windings each having a plurality of vernier tap contacts, a movable vernier contact for successively engaging said vernier tap contacts, and means for so interlocking the motions of said movable contacts that a main movable contact is moved only when the movable vernier contact is engaging a vernier tap contact on the vernier winding which is connected to the other main movable contact.

3. A transformer tap-changing-under-load system comprising, in combination, a main transformer winding provided with a plurality of substantially equally electrically spaced main contacts, a pair of mainmovable contacts, means for causing said main contacts to make successive electrical connection to said main taps in stepclose order whereby for one direction of operation one main contact leads in going from tap to tap and the other main contact makes the same tap change after the first one has completed it and before the first one makes a second tap change, a pair of insulated vernier windings on said main transformer, means for connecting a terminal of one vernier winding to one of said main movable contacts and for connecting a terminal of the other vernier winding to the other main movable contact, a plurality of substantially equally electrically spaced vernier taps on each of said vernier windings, the vernier tap to tap voltage being a fraction of the main tap to tap voltage and being substantially equal to the difference between the main tap to tap voltage and the sum of the vernier tap to tap voltages, vernier tap-changing means for sequentially making connection to said vernier taps Without interrupting the circuit through said means, and means for interlocking said vernier tap-changing means with said main movable contacts in such a way that each main movable contact is only moved from tap to tap when said vernier tap-changing means is in contact with a tap on the vernier winding which is connected to the other main movable contact.

4. A transformer tap-changing-under-load system comprising, in combination, a main transformer winding provided with a plurality of electrically spaced taps, a circuit which is completed through said main winding, two auxiliary windings, each one having at least two terminals, means to connect a terminal of one of said auxiliary windings selectively to one of said taps, means to connect a terminal of the other auxiliary windings selectively to one of said taps, and means to connect a conductor of said circuit selectively to a terminal of said auxiliary windings.

5. A transformer ratio adjusting system comprising, in combination, a main transformer winding equipped with taps, a circuit which is completed through said main winding, two auxiliary windings, connection changing means to connect said auxiliary windings selectively to a tap of said main winding, connection changing means to connect selectively said auxiliary windings to a conductor of said circuit, and means to so interlock the operations of said two connection changing means that the change of a connection through the first connection changing means is effected while the circuit of that connection is interrupted through said second connection changing means.

6. A transformer ratio adjusting system comprising, in combination, a main transformer winding equipped with a plurality of coarse tap steps, a circuit which is completed through said main winding, two auxiliary windings equipped with a plurality of fine tap steps, a ratio adjustor to connect selectively said auxiliary windings to a tap of said main winding, a ratio adjuster to connect a conductor of said circuit selectively to a tap of said auxiliary windings, and means for so interlocking the motions of said two adiustors that a current interruption due to a tap-changing takes place only in the adjustor operating on said fine tap steps.

'7. A transformer tap-changing-under-load system comprising, in combination, a main transformer winding equipped with a plurality of electrically spaced tap contacts, a pair of main movable contacts for successively engaging said main tap contacts, a pair of auxiliary windings connected respectively to said main movable contacts and equipped with electrically spaced contacts, an auxiliary movable contact for successively engaging the contacts of said auxiliary windings, and means for so interlocking the motions of said main and auxiliary movable contacts that a main movable contact moves only when the auxiliary movable contact is in series circuit relation ship with the other main movable contact.

8. A transformer tap-changing-under-load sys tem comprising, in combination, a main transformer winding equipped with a plurality of electrically spaced taps, two auxiliary windings, each one of said auxiliary windings having a voltage a friction of the tap to tap voltage of said main winding, means to connect one end of one of said auxiliary windings selectively to one of said taps with the voltages of said main winding and said auxiliary windng in additive relationship, means to connect one end of the other auxiliary winding selectively to one of said taps with the winding in subtractive relationship, and means to complete a circuit for said main winding through said auxiliary windings selectively.-

excluding said second winding from said circuit,

changing taps on said third winding so as to vary "the number of turns thereof in said circuit, completing said circuit through said second winding and a still different number of turns of said first winding while excluding said third winding from said circuit, andagain changing said taps on said second wnding so as to vary the number of turns thereof in said circuit.

LOUIS F. BLUME.

CERTIFICATE OF CORRECTION.

Patent .No. 2,200,979. m 11;, 191m.

.LOUIS F. BLUME.

Itis hereby certified that error appears in the printedspecification 7 of theabove numbered pat ent requiring correction as follows: Page 5, second column, line 60, olaim 7, forthe words "relation ship", read -4-re1ation'ship*-; line 67., claim 8, for "frictiofl read "fraction-4 line 71;, same oiaim,

befor'e "winding" insert --main-.-; and that the said Letters Patent should be, read with this correction therein that the same may conform'to the rec 0rd of the case in the: Patent Office- Signed-and sealed this 18th day of June, A. D. 1911.0.

. Henry Van Arsdal'e, (Seal) Acting Commissionerof Patents. 

